1. Field of the Invention
The present patent application for industrial invention relates to a compound for realization of modified bitumen.
Although the term “bitumen” will be prevailingly used in the description below, it is understood that the present invention extends to the field of asphalts, in particular for road surfaces.
2. Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 37 CFR 1.98.
Bitumens are complex thermoplastic products composed of very different elements: asphaltenes and malthenes. Bitumens have excellent adhesive properties, but poor mechanical properties, especially according to temperature. In fact, bitumens have a very low hardness at ambient temperature (25° C.). Moreover, at temperatures below 0° C. (cold), bitumens are rigid and fragile, whereas at temperatures above 38° C. (hot), bitumens are plastic, soft and very adhesive. For this reason, bitumens cannot be used for most road or building applications.
The modification of bitumens by means of chemical and polymer additives is extremely important in order to essentially modify the nature of bitumens, thus making modified bitumens suitable for the most diverse industrial uses.
The modification of asphalts and bitumens using granules derived from grinding end-of-life tires is known. The advantages that can be obtained from these initiatives are both of technical and environmental nature.
The technical benefits derive from the performance of bitumen modified with the addition of crumb rubber, i.e. noise reduction, longer life time of finished products, considerably increased elasticity, reduction of fractures and their propagation in manufactured items. Obviously, the above is according to the capacity of crumb rubber to get wet because of the host bitumen. In other words, rubber particles must swell and in chemical-physical terms this means that the solubility parameter of the two products (rubber and bitumen) must be numerically very close so that the solvent part of bitumen, the malthenic fraction, can penetrate the solid particles of rubber granules and form, outside the solid particle, a practically gelatinous phase that is very active in adhesion and cohesion with the remaining bitumen part. For example, Nitrile Rubber (NBR) swells considerably less in bitumens than Styrene-Butadiene-Rubber (SBr). Therefore, with the same concentration and granulometry, the performance of bitumen modified with NBR granules will be considerably lower than the one of bitumen modified with SBr granules.
The environmental benefits derive from the possibility of using a material that can be hardly used in other activities and is available in large quantities, in highly technological applications, replacing elastomer polymers of high value and cost.
An interesting modification of bitumens that has been discovered recently relates to the use of a devulcanized variant of rubber granules. This variant allows for producing a portion of material with low molecular weight, soluble in bitumen or asphalt and allows for creating a surface of the residual granule more suitable for cohesion with bitumen, consequently improving the final mechanical characteristics. However, such a technology is expensive and requires the use of specific equipment, such as pirolizers or extruders especially designed to obtain conversion from mechanical to thermal energy in order to achieve the temperatures that are necessary for resolution of intra and intermolecular bonds of vulcanized products. Moreover, such a technology uses ground products from tires with very high granulometry.
It must be considered that granulometry of ground products obtained from end-of-life tires or other similar vulcanized materials, such as for instance shoe soles, rubber hoses, anti-vibrating unions and washer or dishwasher gaskets, are much higher than a minimum size of 0.5 millimeters. Their polymer bases are generally composed of copolymers of Styrene-Butadiene, (SBr), Acryl-Nitrile Butadiene (NBr), Ethylene-Propylene-Diene (EPDM), Natural Rubber (NR) and Butadiene Polymers (Br). Granulometry higher than 0.5 millimeters considerably reduces the capability of vulcanized rubber powders to obtain radical changes of bitumens.
A process known as “dry process” is currently known for production of modified asphalt. Said process provides for using powders derived from grinding vulcanized products (generally tires) with size higher than 0.4 mm, and the replacement of part of mineral grit in asphalt with said powders. Said powders are also used to produce Rubber Asphalt obtained with wet process (in wet phase) to obtain bitumens with better rheological characteristics than basic bitumen. However, the asphalts and bitumens obtained with the known processes are not suitable to obtain the performance that is currently required by national or international specifications for specific applications in the road or building fields.
Several documents describe bitumens modified with recycled tire powder:                SINIS “Literature review of recycling of by-product in road construction in Europe”        AHMED “Use of Waste materials in Highway construction”        US department of transportation “Crumb Rubber Modifier, Workshop Notes”        JEONG “Interaction effects of crumb rubber modified asphalt binders”        
These documents, however, do not describe the production of a specific extruded compound to modify asphalts and do not specify the quantities of the various components in order to obtain a specific performance of asphalts.
It is known that bitumens modified with crumb rubber of recycled tires are impaired by compatibilization problems of crumb rubber with bitumen. Such an inconvenience is solved by using catalysts mixed in bitumen.
WO20011/074003 discloses the use of a catalyst for FCC (Catalytic Cracking) plant comprising oil and low value polymers, such as polyolefin polymers. Surely SBS is not a low value polymer.
KHALDOUN “Effect of furfural activated crumb rubber on the properties of rubberized asphalt” describes the use of a furfural catalyst to improve adhesion of crumb rubber to bitumen.
According to the prior art the best performance of modified bitumens is obtained with thermoplastic block copolymers Styrene-Butadiene-Styrene (SBS) in linear or radial configurations that are the most used polymer products for bitumen modification. In fact, said thermoplastic block copolymers (SBS) are the best performing ones in bitumen modification, allowing for achieving the desired characteristics of high temperature softening, penetration at ambient temperature, and low temperature flexibility.
Other block copolymers can be used in bitumen modifications, like SBS. They are block copolymer Styrene-lsoprene-Styrene (SIS) and their hydrogenated derivatives SEBS and SEPS, in addition to other block copolymers that can be obtained with modification of the elastomeric phases not based on Butadiene and Isoprene mixtures, but scarcely used in practice because of high cost.
Thermoplastic homo, copo- or ter-polymers are used and usable for bitumen modifications. They are obtained from monomers, such as Ethylene-Vinyl Acetate (EVA), Ethylene-Propylene (EPM), Ethylene-Propylene-Diene (EPDM), Atactic and Isotactic Propylene (PPa/iso), Polyethylene (LLDPE, HDPE, LDPE), Polybutadiene and Polybutene, but none of them, either individually or in combination, can give characteristics similar to SBS.
BAHA “Laboratory comparison of crumb-rubber and SBS modified bitumen and hot mix asphalt” describes a comparison between crumb-rubber modified bitumen and SBS modified bitumen. The conclusion of this document is that SBS modified bitumen has much better performance than crumb rubber modified bitumen. Therefore, in order to replace SBS with crumb rubber, while maintaining the same asphalt performance, 1:3 ratio must be applied, meaning that the quantity of crumb rubber must be at least triple than SBS. This is confirmed by the products found on the market. In fact, SBS modified bitumens generally have SBS quantity of 10% in weight. Instead, crumb rubber modified bitumens have a crumb rubber quantity of 30% in weight.
U.S. Pat. No. 6,818,687 discloses an SBS or SBr modified bitumen after vulcanization and grinding; it is not said that bitumen is simultaneously SBS and SBr modified. Such bitumen has storage problems and therefore a viscosity regulator (oil) and a catalyst with acid and sulphurous base are added.
WO2008/083451 discloses a product comprising SBS, crumb rubber and vulcanizing, plasticizing, lubricating and expanding agents. A thermosetting product is obtained and vulcanized. Therefore, said product is not a thermoplastic asphalt-soluble product. In fact, such a product is used to manufacture shoe soles and crumb rubbers is given as filler, i.e. it can be any material that needs not to have special reactions to obtain special technical characteristics. In any case, shoe soles are obtained via molding, not extrusion.